Average sampling offset estimate before adjusting timing to be more robust against EVA and ETU fading

lib/include/srslte/interfaces/ue_interfaces.h

@@ -497,6 +497,8 @@ typedef struct {
   float cfo_loop_bw_ref;
   float cfo_loop_ref_min;
   float cfo_loop_pss_tol;
+  float sfo_ema;
+  uint32_t sfo_correct_period;
   uint32_t cfo_loop_pss_conv;
   uint32_t cfo_ref_mask;
   bool average_subframe_enabled;

lib/include/srslte/phy/ue/ue_sync.h

@@ -61,6 +61,8 @@
 #include "srslte/phy/common/timestamp.h"
 #include "srslte/phy/io/filesource.h"
 
+#define DEFAULT_SAMPLE_OFFSET_CORRECT_PERIOD  10
+#define DEFAULT_SFO_EMA_COEFF                 0.1
 
 #define DEFAULT_CFO_BW_PSS  0.05
 #define DEFAULT_CFO_PSS_MIN 400  // typical bias of PSS estimation.
@@ -140,7 +142,6 @@ typedef struct SRSLTE_API {
   int next_rf_sample_offset;
   int last_sample_offset; 
   float mean_sample_offset; 
-  float mean_sfo; 
   uint32_t sample_offset_correct_period;
   float sfo_ema; 
   
@@ -248,8 +249,11 @@ SRSLTE_API float srslte_ue_sync_get_sfo(srslte_ue_sync_t *q);
 
 SRSLTE_API int srslte_ue_sync_get_last_sample_offset(srslte_ue_sync_t *q); 
 
-SRSLTE_API void srslte_ue_sync_set_sample_offset_correct_period(srslte_ue_sync_t *q, 
+SRSLTE_API void srslte_ue_sync_set_sfo_correct_period(srslte_ue_sync_t *q,
-                                                                uint32_t nof_subframes); 
+                                                      uint32_t nof_subframes);
+
+SRSLTE_API void srslte_ue_sync_set_sfo_ema(srslte_ue_sync_t *q,
+                                           float ema_coefficient);
 
 SRSLTE_API void srslte_ue_sync_get_last_timestamp(srslte_ue_sync_t *q, 
                                                   srslte_timestamp_t *timestamp);

lib/src/phy/ue/ue_sync.c

@@ -41,11 +41,9 @@
 
 #define MAX_TIME_OFFSET 128
 
-#define TRACK_MAX_LOST          100
+#define TRACK_MAX_LOST          10
 #define TRACK_FRAME_SIZE        32
 #define FIND_NOF_AVG_FRAMES     4
-#define DEFAULT_SAMPLE_OFFSET_CORRECT_PERIOD  0
-#define DEFAULT_SFO_EMA_COEFF                 0.1
 
 
 cf_t dummy_buffer0[15*2048/2];
@@ -386,7 +384,7 @@ int srslte_ue_sync_set_cell(srslte_ue_sync_t *q, srslte_cell_t cell)
       srslte_sync_set_em_alpha(&q->sfind,   1);
       srslte_sync_set_threshold(&q->sfind,  3.0);
 
-      srslte_sync_set_em_alpha(&q->strack,  0.2);
+      srslte_sync_set_em_alpha(&q->strack,  0.0);
       srslte_sync_set_threshold(&q->strack, 1.2);
 
     }
@@ -464,14 +462,14 @@ void srslte_ue_sync_set_cfo_tol(srslte_ue_sync_t *q, float cfo_tol) {
 }
 
 float srslte_ue_sync_get_sfo(srslte_ue_sync_t *q) {
-  return q->mean_sfo/5e-3;
+  return q->mean_sample_offset/5e-3;
 }
 
 int srslte_ue_sync_get_last_sample_offset(srslte_ue_sync_t *q) {
   return q->last_sample_offset; 
 }
 
-void srslte_ue_sync_set_sample_offset_correct_period(srslte_ue_sync_t *q, uint32_t nof_subframes) {
+void srslte_ue_sync_set_sfo_correct_period(srslte_ue_sync_t *q, uint32_t nof_subframes) {
   q->sample_offset_correct_period = nof_subframes; 
 }
 
@@ -563,7 +561,7 @@ static int track_peak_ok(srslte_ue_sync_t *q, uint32_t track_idx) {
   uint32_t frame_idx = 0; 
   if (q->sample_offset_correct_period) {
     frame_idx = q->frame_ok_cnt%q->sample_offset_correct_period;
-    q->mean_sample_offset += (float) q->last_sample_offset/q->sample_offset_correct_period;
+    q->mean_sample_offset = SRSLTE_VEC_EMA((float) q->last_sample_offset, q->mean_sample_offset, q->sfo_ema);
   } else {    
     q->mean_sample_offset = q->last_sample_offset; 
   }
@@ -590,22 +588,11 @@ static int track_peak_ok(srslte_ue_sync_t *q, uint32_t track_idx) {
     // Adjust RF sampling time based on the mean sampling offset
     q->next_rf_sample_offset = (int) round(q->mean_sample_offset);
 
-    // Reset PSS averaging if correcting every a period longer than 1
-    if (q->sample_offset_correct_period > 1) {
-      srslte_sync_reset(&q->strack);
-    }
-    
-    // Compute SFO based on mean sample offset 
-    if (q->sample_offset_correct_period) {
-      q->mean_sample_offset /= q->sample_offset_correct_period;
-    }
-    q->mean_sfo = SRSLTE_VEC_EMA(q->mean_sample_offset, q->mean_sfo, q->sfo_ema);
-
     if (q->next_rf_sample_offset) {
-      INFO("Time offset adjustment: %d samples (%.2f), mean SFO: %.2f Hz, %.5f samples/5-sf, ema=%f, length=%d\n", 
+      INFO("Time offset adjustment: %d samples (%.2f), mean SFO: %.2f Hz, ema=%f, length=%d\n",
            q->next_rf_sample_offset, q->mean_sample_offset,
            srslte_ue_sync_get_sfo(q), 
-           q->mean_sfo, q->sfo_ema, q->sample_offset_correct_period);    
+           q->sfo_ema, q->sample_offset_correct_period);    
     }
     q->mean_sample_offset = 0; 
   }

srsue/hdr/phy/phch_common.h

@@ -65,7 +65,6 @@ public:
   float cur_radio_power;
   float cur_pusch_power;
   float avg_rsrp;
-  float avg_rsrp_cqi;
   float avg_rsrp_dbm;
   float avg_rsrq_db;
   float avg_rssi_dbm;

srsue/src/main.cc

@@ -187,6 +187,14 @@ void parse_args(all_args_t *args, int argc, char *argv[]) {
      bpo::value<int>(&args->expert.phy.cqi_fixed)->default_value(-1),
      "Fixes the reported CQI to a constant value. Default disabled.")
 
+    ("expert.sfo_correct_period",
+     bpo::value<uint32_t>(&args->expert.phy.sfo_correct_period)->default_value(DEFAULT_SAMPLE_OFFSET_CORRECT_PERIOD),
+     "Period in ms to correct sample time")
+
+    ("expert.sfo_emma",
+     bpo::value<float>(&args->expert.phy.sfo_ema)->default_value(DEFAULT_SFO_EMA_COEFF),
+     "EMA coefficient to average sample offsets used to compute SFO")
+
     ("expert.snr_ema_coeff",
      bpo::value<float>(&args->expert.phy.snr_ema_coeff)->default_value(0.1),
      "Sets the SNR exponential moving average coefficient (Default 0.1)")

srsue/src/phy/phch_common.cc

@@ -344,7 +344,6 @@ void phch_common::reset() {
   cur_pusch_power = 0;
   avg_snr_db_cqi = 0;
   avg_rsrp = 0;
-  avg_rsrp_cqi = 0;
   avg_rsrp_dbm = 0;
   avg_rsrq_db = 0;
 

srsue/src/phy/phch_recv.cc

@@ -683,6 +683,10 @@ void phch_recv::set_ue_sync_opts(srslte_ue_sync_t *q, float cfo)
     srslte_sync_set_cfo_cp_enable(&q->sfind, false, 0);
   }
 
+  // Set SFO ema and correct period
+  srslte_ue_sync_set_sfo_correct_period(q, worker_com->args->sfo_correct_period);
+  srslte_ue_sync_set_sfo_ema(q, worker_com->args->sfo_ema);
+
   sss_alg_t sss_alg = SSS_FULL;
   if (!worker_com->args->sss_algorithm.compare("diff")) {
     sss_alg = SSS_DIFF;

srsue/src/phy/phch_worker.cc

@@ -407,7 +407,7 @@ void phch_worker::work_imp()
   update_measurements();
 
   if (chest_ok) {
-    if (phy->avg_rsrp_dbm > -130.0 && phy->avg_snr_db_cqi > 0.0) {
+    if (phy->avg_rsrp_dbm > -130.0 && phy->avg_snr_db_cqi > -6.0) {
       log_h->debug("SNR=%.1f dB, RSRP=%.1f dBm sync=in-sync from channel estimator\n",
                    phy->avg_snr_db_cqi, phy->avg_rsrp_dbm);
       chest_loop->in_sync();
@@ -1433,7 +1433,7 @@ void phch_worker::update_measurements()
     }
 
     // Average RSRP taken from CRS
-    float rsrp_lin = srslte_chest_dl_get_rsrp_neighbour(&ue_dl.chest);
+    float rsrp_lin = srslte_chest_dl_get_rsrp(&ue_dl.chest);
     if (isnormal(rsrp_lin)) {
       if (!phy->avg_rsrp) {
         phy->avg_rsrp = SRSLTE_VEC_EMA(rsrp_lin, phy->avg_rsrp, snr_ema_coeff);
@@ -1473,17 +1473,7 @@ void phch_worker::update_measurements()
       }
     }
 
-    // To compute CQI use RSRP measurements from resource elements in RS since is more robust to time offset
+    phy->avg_snr_db_cqi  = 10*log10(phy->avg_rsrp/phy->avg_noise);
-    float rsrp_lin_cqi = srslte_chest_dl_get_rsrp(&ue_dl.chest);
-    if (isnormal(rsrp_lin_cqi)) {
-      if (!phy->avg_rsrp_cqi) {
-        phy->avg_rsrp_cqi = SRSLTE_VEC_EMA(rsrp_lin_cqi, phy->avg_rsrp_cqi, snr_ema_coeff);
-      } else {
-        phy->avg_rsrp_cqi = rsrp_lin_cqi;
-      }
-    }
-
-    phy->avg_snr_db_cqi  = 10*log10(phy->avg_rsrp_cqi/phy->avg_noise); 
 
     // Store metrics
     dl_metrics.n      = phy->avg_noise;

srsue/ue.conf.example

@@ -153,6 +153,8 @@ enable = false
 #                       good for long channels. For best performance at highest SNR reduce it to 1.  
 # sfo_correct_disable:  Disables phase correction before channel estimation to compensate for 
 #                       sampling frequency offset. Default is enabled. 
+# sfo_ema:              EMA coefficient to average sample offsets used to compute SFO
+# sfo_correct_period:   Period in ms to correct sample time to adjust for SFO
 # sss_algorithm:        Selects the SSS estimation algorithm. Can choose between
 #                       {full, partial, diff}. 
 # estimator_fil_auto:   The channel estimator smooths the channel estimate with an adaptative filter.
@@ -210,6 +212,8 @@ enable = false
 #equalizer_mode      = mmse
 #time_correct_period = 5
 #sfo_correct_disable = false
+#sfo_ema             = 0.1
+#sfo_correct_period  = 10
 #sss_algorithm       = full
 #estimator_fil_auto  = false
 #estimator_fil_stddev  = 1.0